I had my pool re-plastered about 2 months ago. I have been using the BBB method and the TF-100 test kit since it was re-plastered.
I suspected the results I was getting for my CH levels was too high using the TF-100 test kit.
I took water samples to 4 pool stores. The results were 220, 220, 285 and 320 for the CH level. My testing showed an range of 430 – 460.
I went back to two of the pool stores using Taylor chemicals and asked them to retest while I was watching. Both again got 220 CH levels.
Thinking my chemicals might be bad I purchased the Taylor chemicals from them. I retested at home using the new chemicals. I got 410 instead of 440. I retested and got 440.
Since I was getting inconsistent results, I decided it was probably something I was doing.
I then remembered one of the instructions I was not following in the Extended Test Kit Directions extended-test-kit-directions-t25081.html
“Hold the dropper bottles vertically and squeeze gently, so that drops come out slowly and seem to hang on the tip of the dropper bottle for a moment before falling."
I was holding the bottle at a 20-30 degree angle and squeezing out the drops. I think I started out holding the bottle vertically but over the last 2 months changed to holding it at 20-30 degrees.
I reran the test holding bottles vertically. The CH level dropped to 310 with both the set of chemicals from the pool store and the chemicals from the TF-100 test kit.
As to why the pool store got 220 CH levels using the Taylor chemicals I think the bottle they were using has a bigger hole for the drops (thus bigger drops) than the “Taylor R-0012 bottle and the TF100 R-0012 bottle. They were not using the Taylor bottle to dispense the drops.
I measured the amount of difference for 30 drops of R-0012 by holding the bottle vertically (1.2 ml) versus holding it a 20-30 degree angle (.9 ml). I used a 2.5 ml syringe I got from the drug store to measure the amount. Holding the bottle at a 20-30 degree angle results in about 25% less volume dispensed which explains why my results were so high. Using the syringe is probably not exact but it’s close enough to show the problem.